Origin of the atmosphere

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Origin of the atmosphere

• The original atmosphere
• Probably made up of hydrogen and helium.
• These are fairly common in the universe.
• Original atmosphere stripped away by the solar
  wind
• H and He are very light
• Hydrogen and helium have the smallest atoms by
  mass.
• The early earth was not protected by a magnetic
  field.

2
The secondary atmosphere

• Formed from degassing of volcanoes
• Gasses emitted probably similar to the gasses
  emitted by volcanoes today.
• H2O (water), 50-60
• CO2 (carbon dioxide), 24
• SO2 (sulfur dioxide), 13
• CO (carbon monoxide),
• S2 (sulfur),
• Cl2 (chlorine),
• N2 (nitrogen),
• H2 (hydrogen),
• NH3 (ammonia) and
• CH4 (methane)

3
Modern atmosphere

• Nitrogen (N2)-
• 78,
• Oxygen (O2)-
• 21,
• Carbon Dioxide (CO2) 0.03 ,
• Where did all the oxygen come from?

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Volcanic outgassing Modern Atmosphere
H2O 50-60 N2 78
CO2 24 O2 21
SO2 13 CO2 0.03

1. Where did all the O2 come from?
2. Where did all the CO2 go?

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Formation of the oceans

• The earth is cool enough that H2O condenses to
  form the oceans.
• Estimates of the amount of H2O outgassed is not
  enough to fill the oceans
• It seems likely that a large volume of water was
  added by the impact of icy meteors on the
  atmosphere.
• CO2 dissolves into the oceans.

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In the oceans life evolves

• Ingredients necessary for life
• NH3 ammonia
• CH4 Methane
• H2O Water
• These can produce amino acids, the building
  blocks of life

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• Life may have originated
• at hydrothermal vents deep in the oceans

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Life changes the atmosphere

• With the evolution of life the first cellular
  organisms (cyanobacteria) began to use the gasses
  in the early atmosphere (NH3 ammonia, CH4
  methane, H2O water) for energy.

Photosynthetic organisms evolve. These
organisms use CO2 and produce oxygen (O2) as a
waste product.
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• Where did the O2 come from?
• Produced by photosynthetic life.
• Where did the CO2 go?
• Dissolves in water in the oceans
• Used by life by photosynthesis and buried when
  plants and micro-organisms die.
• The source of coal and oil

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Early history of life and the atmosphere

• The Earth is about 4.5 billion years old.
• Life first appears in the oceans at least 3.5
  billion years ago.
• 0.9 billion years ago there is enough oxygen in
  the atmosphere to produce the ozone layer and
  life can finally move onto land.
• The ozone layer protects the earth from harmful
  ultra violet radiation from the sun.

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How do we know??

• Data from instruments
• Written accounts
• fossil data

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Summary
1st atmosphere H and He from solar nebula Lost to solar wind
2nd atmosphere H20, CO2 and SO2 from volcanic degassing Transformed by photosynthesis
Current atmosphere N2, O2, from photosynthesis and constant N2 production
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Under todays warm up

• Draw a timeline with 4 pictures of the early
  earth atmosphere and characteristics

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Layers of atmosphere
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Layers of the atmosphere

• There are 4 MAIN layers in the atmosphere
• They are the troposphere, mesosphere,
  thermosphere, and stratosphere
• detailed next

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Troposphere

• This is the layer that is closest to the surface
  of the earth
• Its elevation ranges from 0 to 10 km
  (0-7miles)
• Weather occurs here

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Tropopause

• Boundary between troposphere and stratosphere
• Isothermal layer (temp remains stable)
• Jet stream occurs here

18
Stratosphere

• This layer sits on top of the troposphere
• Its elevation ranges from 10 km to around 25 km
  (7-13 miles)
• This layer contains the O3, protecting us from UV
  radiation
• Almost completely free of clouds weather
• We can fly herewhy?

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Stratopause

• Isothermal layer (temp remains stable)
• Separating stratosphere and mesosphere

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Mesosphere

• This layer is above the stratosphere
• Its elevation ranges from 25 to 100 km
  (31-50miles above surface)
• Freezes water vapor into ice clouds
• Meteors burn up here (shooting stars)

21
Mesopause

• Isothermal layer
• Separates mesosphere and thermosphere

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Thermosphere

• Aka Ionosphere
• This is the highest layer of the atmosphere
• Its height ranges from 100 to 400 km
• Gamma rays, x-rays, and UV bombard molecules
• the location in the atmosphere that the northern
  lights occur (aurora borealis)

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Composition of Air

• There are many different types of gasses in the
  atmosphere
• They include nitrogen, oxygen, argon, carbon
  dioxide and other noble gasses
• The gas that is most abundant is nitrogen

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And, the bad stuff

• Nitrous oxide N2O 0.00003
• Concentration increases 0.3 each year due to
  fossil fuels, fertilizers, burning of biomass,
  soil fertilization
• Humans contribute 6,000 tons/yr
• Nature contributes 20,000 tons/yr

• Ozone O3 0.000005
• 97 found in stratosphere
• Absorbs UV radiation
• Produced with photochemical smog
• O3 is decreasing primarily due to CFCs